At present, no vaccine against group A Streptococcus (GAS, S. pyogenes) exists. This Gram-positive bacterial pathogen is a leading cause of global morbidity and mortality. With an estimated >500,000 annual deaths, GAS ranks among the top 10 causes of mortality from infectious disease. The extraordinary antigenic variability of the M protein, the most abundant and antigenic protein on the GAS surface, has been a major impediment in the development of such a vaccine. Sequence variation is localized to N-terminal portions of the mature M protein, and in particular, a region denoted the hypervariable region (HVR) that distinguishes one M type from another. More than 220 distinct M HVRs have been identified. The hypervariability of this region is ascribable to immune pressure, as the HVR is a target of opsonizing antibodies. Such antibodies are generally type-specific, recognizing the immunizing M type but not other M types. A biologically inspired solution to this problem is suggested by our recent ground-breaking work (Buffalo et al., Nat Micro), which revealed the existence of functionally conserved sequence patterns that are hidden within the HVRs of a large number of M proteins. These conserved sequence patterns are required for the indispensable function of recruiting the inhibitory complement factor C4b-binding protein (C4BP) to the GAS surface. The type-promiscuity of C4BP contrasts sharply with the type-specificity displayed by antibodies. We seek in this proposal to ask the simple but critical question of whether antibodies can be generated that mimic the type-promiscuous binding mode of C4BP and thereby provide broadly neutralizing immunity. Compelling evidence exists to support the hypothesis that an M protein antigen containing just the conserved and essential C4BP- binding pattern will evoke a broadly neutralizing response. In Aim 1, we will ?refocus? antibody recognition from antigenically variable amino acids in M protein HVRs to conserved C4BP-binding ones. We will do this by minimizing protein constructs to the short C4BP-binding sequence pattern, and verify that these constructs retain the dimeric, ?-helical coiled-coil structure and C4BP-binding of native M protein HVRs. In Aim 2, we will ask whether these minimized M protein HVR constructs evoke broad neutralizing immunity against M proteins containing the C4BP-binding sequence patterns. These studies will be carried out through the multi-PD/PI mechanism with PIs Partho Ghosh and Victor Nizet. A uniquely synergistic and long-standing collaboration exists between the complementary efforts of the Ghosh (biochemistry and structural biology) and Nizet (bacterial pathogenesis and innate immunity) laboratories in studying GAS virulence from atoms to animals.